Login Server integration, cleanup

- Added client configuration (client.json) and ClientConfig class
- Renamed PacketHello to PacketHandshake, some restructuring
- Added base64 en/de-coder
- Client can now create accounts on the login-server
- Added sha512 and string_to_hex functions
- Added HTTPResponse.asJSON
- Added proof-of-work for login-server requests,
- Added LoginServer.createAccount
- Added TCPClient function-hooks
- Added loadJSONFile utility function
- Commented some general stuff